1. Field of the Invention
The present invention relates to a method for production of an electroless plating material that is used for forming a plating film on its resin surface by an electroless plating treatment.
2. Description of the Related Art
Resin materials are expected to be used in a wide variety of fields because of their characteristics such as high formability, high degree of freedom for characteristic values such as strength, and light weight. However, resins also have disadvantages such as lack of electrical conductivity and low hardness. Thus, for the purpose of compensating for the disadvantages of resin materials, resins are combined with other materials such as metals. For example, one well-known method for imparting electrical conductivity to a resin is to form an electrically-conductive film such as metal film on a surface of the resin. Above all, chemical plating (electroless plating) can form an electrically-conductive film easily and inexpensively as compared with other methods for forming an electrically-conductive film. Electroless plating is a process where a metal film is formed on a material surface by chemically reducing and depositing metal ions in a solution. In contrast to electrolytic plating in which a metal film is formed by electrodeposition that is induced by electricity power, a metal film can be formed even on insulating materials such as resins. In addition, resin materials with a metal film formed thereon can be further subjected to electrolytic plating and can therefore be used in a wide variety of applications. Thus, the electroless plating treatment is widely used as a method for imparting electrical conductivity or metallic luster to resin materials for use in the fields of automobile parts, electric appliances and so on.
However, the films formed by electroless plating have problems because it takes a long time to form the films and because the adhesion of the films to resin materials is not sufficient. Thus, a pretreatment is often applied to resin materials prior to the electroless plating treatment.
As a pretreatment to improve adhesion, roughening of a resin material surface by chemical etching is typically carried out for the purpose of improving adhesion strength between the resin material and the plating film by an anchor effect. However, the method of surface roughening by chemical etching not only decreases the surface smoothness, but also poses a problem in terms of disposal of waste liquid because toxic and deleterious substances such as chromic acid, permanganic acid, and sulfuric acid are used.
Accordingly, an electroless plating film is formed after a surface of the resin material has been modified by bringing the resin material with ozone water (ozone water treatment) in Japanese Patent Application Publication No. 2005-36292 (JP-A-2005-36292), Japanese Patent Application Publication No. 2005-113236 (JP-A-2005-113236) and Japanese Patent Application Publication No. 2009-24244 (JP-A-2009-24244). When a resin material is brought into contact with ozone water, molecular chains such as double bonds are broken by oxidation by ozone in a surface of the resin material and polar groups such as OH groups, CO groups, and COOH groups are formed in the surface. When a resin material that has many polar groups in its surface is subjected to electroless plating, a plating film that has excellent adhesion strength can be formed. In addition, when the ozone water penetrates into a surface region of the resin material, a layer that has pores of below nano-level is formed in the surface of the resin. When electroless plating is carried out on such a surface of the resin material, the plating solution penetrates even into the pores. Since metal ions are deposited in the pores to form a mixed layer composed of the resin and metal in the surface region of the resin material, a nano-level anchor effect may be achieved.
In the above documents, the surface of the resin material is subjected to, in addition to an ozone water treatment, ultraviolet irradiation. It is said to be preferred to carry out the ultraviolet irradiation simultaneously with the ozone water treatment because the surface of the resin material is activated and polar groups are formed by a synergetic effect of ultraviolet rays and ozone.
As with the above, a surface treatment is carried out using a solution that contains an alkaline component after a treatment of the resin material using ozone water for the purpose of exposing a large number of polar groups to the surface of a resin material. When a solution that contains an alkaline component is used, however, there is caused a problem that the resin material is not dissolved or the resin is so soluble that it is dissolved more than necessary and, worse yet, the resin material itself is deteriorated depending on the combination of the alkali and resin that are used. In addition, a surface treatment of a resin material using a solution that contains an alkaline component is equivalent to the chemical etching that is described above and is apt to decrease the smoothness of the surface of the resin material.
That is, the treatment with the alkaline component just activates a surface of a resin material to form a large number of polar groups so that the plating treatment can be carried out on the surface of the resin material with high adhesion. No evaluation has been made on the adhesion strength in resin materials that have been left to stand in a severe environment after the plating treatment.
The adhesion of an electroless plating film to a flat resin surface can be achieved even by a mere treatment of the resin material with ozone water prior to the electroless plating treatment. However, the result of a durability test that was conducted on such electroless plating coated members reveals that incidents of peeling of electroless plating films significantly increases when they have been left to stand in a high-temperature and high-humidity environment. Thus, reliability that ensures that the coated members may be used even in an environment where a high-temperature and high-humidity condition is likely to be established is required.